A photosensitive resin composition is used as a material for forming electronic components, optical products or optical elements, a material for forming layers, an adhesive, etc. Particularly, it is suitably used for products or components which are formed through a patterning process using electromagnetic radiation.
For example, polyimide, which is a polymer material, exhibits top-ranking performance in properties such as heat resistance, dimensional stability and insulation property among organic materials. Thus, it is widely used as an insulation material for electronic components, etc., and it is increasingly and actively used as a chip coating film of semiconductor elements, a substrate of flexible printed-wiring boards, and so on.
Also in recent years, to solve problems with polyimide, intensive investigations have been carried out into polybenzoxazole having a low water absorption property a low dielectric constant, polybenzimidazole having excellent adhesion to substrates, and so on, which are processed in a similar manner to polyimide.
In general, polyimide shows poor solubility in solvents and is difficult to process. As the method for patterning polyimide in a desired shape, therefore, there is a method for obtaining a pattern of polyimide by patterning polyimide by exposure to light and development when it is in a state of polyimide precursor that has excellent solubility in solvents, and then imidizing the resultant by heating, etc.
Various methods are proposed for forming a pattern by using a polyimide precursor. Two typical examples are as follows:
(1) A method for forming a pattern by forming a resist layer comprising a photosensitive resin on a polyimide precursor which has no pattern forming ability
(2) A method for forming a pattern by introducing a photosensitive site to a polyimide precursor by a bond or coordination and forming a pattern by its action, or a method for forming a pattern by mixing a polyimide precursor with a photosensitive component to produce a resin composition and forming a pattern by the action of the photosensitive component
Typical patterning methods using method (2) include: (i) a method for obtaining a polyimide pattern in which a naphthoquinonediazide derivative which acts as a dissolution inhibitor before exposure to electromagnetic radiation and which produces a carboxylic acid and acts as a dissolution promoter after the exposure, is mixed with a polyimide precursor (polyamic acid) so that there is an increase in contrast between the dissolution rate of exposed regions in developers and that of unexposed regions in the same, thereby forming a pattern; thereafter, the pattern is imidized to obtain a polyimide pattern (patent literature 1) and (ii) a method for obtaining a polyimide pattern in which a methacryloyl group is introduced to a polyimide precursor via an ester bond or ionic bond; a photoradical generator is added thereto to crosslink exposed regions so that there is an increase in contrast between the dissolution rate of the exposed regions in developers and that of unexposed regions in the same, thereby forming a pattern; thereafter, the pattern is imidized to obtain a polyimide pattern (patent literature 2).
Compared with method (1), method (2) needs no resist layer, so that the process can significantly simplified. However, method (i) is problematic in that the original properties of polyimide cannot be obtained when the added amount of the naphthoquinonediazide derivative is increased for increasing the dissolution contrast. Method (ii) is problematic in that there is a limitation on the structure of the polyimide precursor.
There is a report of other patterning method (iii) which is a method for obtaining a polyimide pattern in which a polyimide precursor (polyamic acid) is mixed with a photobase generator; the mixture is exposed to light and then heated to promote cyclization by the action of bases generated by the exposure and thus to decrease the solubility of the polyimide precursor in developers so that there is an increase in contrast between the dissolution rate of exposed regions in developers and that of unexposed regions in the same, thereby forming a pattern; thereafter, the pattern is imidized to obtain a polyimide pattern (patent literature 3).
Other examples of the photosensitive resin composition comprising a photobase generator include a photosensitive resin composition comprising an epoxy compound (for example, patent literature 4). The photobase generator is exposed to light to generate amines in a layer that contains the epoxy compound, so that the amines act as an initiator or catalyst and cure the epoxy compound in exposed regions only, thereby forming a pattern.